When measuring formation pressure, it is demanded that the precise value of formation fluid being obtained within the shortest time period. In order to realize this objective, it is of great importance to precisely control fluid suction volume.
At present, control of the suction amount of the high-pressure fluid mixing pump is mostly realized via a displacement sensor. FIG. 1 is a diagram showing an existing high-pressure fluid mixing pump control system. To obtain precise control of the suction amount, a displacement sensor needs to be installed in the pump suction oil cylinder, and meanwhile a complicated set of control system needs to be designed. Referring to FIG. 1, the control system comprises four mechanical hydraulic valves, various hydraulic components and sensors; the piston cylinder is controlled via various complex compound commands, and meanwhile the displacement sensor is used for metering the displacement distance of the piston, thus achieving the purpose of controlling the suction amount.
Aforesaid existing high-pressure fluid mixing pump control system possesses the following drawbacks: 1) the structure is so complicated that it only can be achieved via various compound commands, thus operation is complex; 2) low precision, a large number of commands need to be given during implementation, and operation staff controls them according to the feedback information from the sensors. Because of the delay of data transmission, the precision is often low, the error is around 10% through the actual measurement; 3) reliability can be affected. Since the hydraulic system is easy to be affected by the external environment, outside interferences, for example, the hydraulic oil is not clean enough, will affect the stable operation of the system, and will even lead to paralysis of the whole control system.
Therefore, there are at least the following technical defects in the prior art: a complicated set of hydraulic control loop has to be designed to coordinate with the use of the displacement sensor, so that the whole hydraulic system is very complicated; at the same time, because of the delay of data transmission, the control precision of fluid volume is also affected and is hard to meet the requirement of high precision. Therefore, the existing high-pressure fluid mixing pump has the problem of low control precision or complex structure, which cannot satisfy well the use demand.